1. Field of the Invention
The present invention relates to an image compression method of compressing a 1-frame image including a plurality of pels by use of different compression algorithms and to an image processing system.
2. Description of the Related Art
An image processing system includes an image input unit for inputting an image, a processing unit for analyzing and processing the inputted image and an output unit for outputting the processed image.
The image processing system effects an image compression to compress original image data down to a less amount of image data in order to process the image at a high efficiency. Note that even when compressing the image, the original image data can be, it is assumed, restored with the less amount of image data.
An image compression methods includes a method of thinning out every second or third image-forming pel. Then, the image restoring method involves copying an image adjacent to the pel thinned out on the thinned-out portion, whereby the original image is restored.
The following is also a method other than the compression method described above. The pels described above assume colors. An color expression requires several bits for color data of R (red), G (green) and B (blue) per pel. For this reason, a 1-frame image contains a considerable amount of color data.
Then, there arises a necessity for a method of compressing the color data quantity down to a less color data quantity to process the image at a good efficiency. The method of compressing the color data quantity embraces, for instance, a compression method of converting colors of all the pels contained in a certain unit area of a certain image into one representative color.
Furthermore, a variety of compression methods may be considered as a method of compressing the color data quantity. In this case, the compression method exhibiting a high compression rate of the color data quantity is demanded. The compression rate herein implies a value obtained by dividing an after-compression color data quantity by a pre-compression color data quantity with respect the pels contained in a certain unit area.
According to the conventional compression methods, however, if a certain unit area containing a plurality of pels is provided, the color data quantity of the unit area is compressed by an arbitrary method. In addition, the relevant unit area is not compressed by a compression method having the highest compression rate. The color data quantity can not therefore be compressed down to a less data quantity.